Change range type of interpolation output

For both, scalar and vector valued data, the interpolation output is
scalar as the dimensionality is captured by the elements of the finite
element basis.

Fixes the issue for the poisson-rt0-p0 test case.
(See commit e7f35164)

dune/functions/functionspacebases/interpolate.hh

@@ -110,6 +110,7 @@ public:
   {
     using FiniteElement = typename Node::FiniteElement;
     using FiniteElementRange = typename FiniteElement::Traits::LocalBasisType::Traits::RangeType;
+    using FiniteElementRangeType = typename FiniteElement::Traits::LocalBasisType::Traits::RangeFieldType;
     using FunctionBaseClass = typename Dune::LocalFiniteElementFunctionBase<FiniteElement>::type;
 
     // Note that we capture j by reference. Hence we can switch
@@ -126,7 +127,7 @@ public:
 
     using FunctionFromCallable = typename Dune::Functions::FunctionFromCallable<FiniteElementRange(LocalDomain), decltype(localFj), FunctionBaseClass>;
 
-    auto interpolationValues = std::vector<FiniteElementRange>();
+    auto interpolationValues = std::vector<FiniteElementRangeType>();
 
     auto&& fe = node.finiteElement();